GABAB receptor mediated inhibition of field stimulation-induced contractions of rabbit bladder muscle in-vitro

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Abstract
The effects of GABA and selective GABAA and GABAB receptor agonists and antagonists have been investigated on field stimulation-induced contractions (0·1 Hz) of rabbit urinary bladder strips in-vitro. Atropine inhibits twitches of bladder strips obtained from the bladder dome more effectively than those obtained from the bladder base. Both GABA and the selective GABAB receptor agonist, (±)-baclofen inhibited field stimulation-induced contractions to about the same extent, while the selective GABAA receptor agonist, homotaurine had no effect. In the presence of atropine, GABA failed to inhibit further the amplitude of twitches. The effects of either GABA or (±)-baclofen were antagonized by the GABAB receptor antagonists homotaurine and 5−aminovaleric acid, while the GABAA receptor antagonist picrotoxin had no effect. Neither GABA nor (±)-baclofen had any significant effect on acetylcholine-induced contractions of unstimulated bladder strips, but they were abolished by atropine. These results suggest that GABAB receptors inhibit field stimulation-induced contractions of rabbit bladder muscle by reducing the amount of acetylcholine released per nerve impulse.